German Patent DE 3346 351 with a publication date of Apr. 9, 1992 describes a plug that is provided at least partially with a teflon coating. Such a plug touches the inside wall of the cylinder with beads that exert a specific pressure on the inside wall of the cylinder, thus ensuring the sealing effect. The beads are designed in such a way that the perpendicular lines of the bead surface that face away from the plug face toward the wall of the barrel. The patent uses teflon to provide a protective surface between the medium and the rubber portion of the plug. This is thus exclusively an insulating function; the excellent sliding properties of teflon are not taken into consideration any further here. In this publication, the term siliconization was not mentioned. It is thus to be assumed that even in this case, one skilled in the art would read this text to mean that this is a syringe that corresponds otherwise to the general technical knowledge (e.g., DIN Standard 13 098, Part 1, Item 4.4) and that is also siliconized on the inside of the cylinder. Autoclaving is not mentioned.
DE-GM 19 73 042 dated Nov. 23, 1967 describes a plastic syringe made of synthetic resin, which consists of a plastic cylinder with a needle opening and a plug opening, a plug, and a plunger. The syringe has, as a basic feature, a shell-shaped or bowl-shaped plug that is made of commercially available material. Such a sealing lip is feasible, however, only in combination with a lubricant, especially with silicone oil. If silicone oil is not present, the sealing lips would be distorted because of the great friction and, giving way to the force, they would tip over. In this publication, the term siliconization also was not mentioned. Thus, it is also to be assumed here that one skilled in the art would read this text to mean that this is a syringe that otherwise corresponds to the general technical knowledge (e.g., DIN Standard 13 098, Part 1, Item 4.4) and that is also siliconized on the inside of the cylinder. Autoclaving is not mentioned.
Patent AT-E 68 979 describes a filled, terminally sterilized syringe. The syringe is made of plastic. The syringe has a cylinder with a distal end with a syringe outlet piece. The syringe outlet piece is sealed with a closure. Before filling, the inside wall of the syringe is coated with silicone oil. After filling, the syringe is sealed with a flexible rubber plug, which is also able to slide into the cylinder because of the silicone oil.
The process for the production of a filled, terminally sterilized syringe thus begins with waste particles or other contaminants being removed from the seal and the plunger. Microbial contaminants on the seal and the plunger are destroyed. The cylinder is washed with a considerable number of water jets to remove pyrogens and waste particles. Then, silicone oil is applied on the inside wall of the syringe. The closure is then slipped onto the syringe outlet piece. The contrast medium is filled in the syringe through the proximal end of the syringe. The syringe is then sealed with the plug. This assembled and filled syringe is sterilized in an autoclave. In this case, in addition to the commonly used autoclave pressure, an additional supporting pressure is generated in the autoclave.
Prefilled, terminally sterilized cartridge-needle units that are provided with a silicone oil layer on the inside wall are known from the publication by Venten and Hoppert (E. VENTEN and J. HOPPERT (1978) Pharm. Ind. Vol. 40, No. 6, pages 665 to 671). The cartridge-needle units, which have a plug on the proximal end, are filled distally via the rolled edge. The rolled edge is then sealed with a sealing disk, whereby a flange cap attaches the sealing disk to the rolled edge. (M. JUNGA (1973) Pharm. Ind. Vol. 35, No. 11a, pages 824 to 829). The prefilled cartridge-needle units are then moved into an autoclave. This autoclave can be adjusted in terms of temperature and pressure.
European Patent Application EP 0553 926 (date of application: Jan. 26, 1993) describes a process for terminal sterilization of a prefilled plastic syringe or glass syringe, whereby the syringe contains a contrast medium. The inside wall of the disposable syringe is coated with silicone oil. The syringe consists of a barrel that has a syringe outlet piece at the distal end. In addition, disposable cartridge-needle units are indicated in the form already described above by Venten and Hoppert. The disposable syringes have an open proximal end, which can be sealed by a plug that can slide into the disposable syringe. The plug is connected to a plunger.
WO 95/12482 describes a process for the production of prefilled plastic syringes that are filled with a contrast medium. The inside wall of the syringe is coated with silicone oil. The syringes consist of a cylinder, a syringe outlet piece at the distal end, which is prepared for a cannula attachment. The syringe also comprises a plug that can slide into the cylinder. It seals the proximal end of the syringe. The syringe was produced according to a process that results in pyrogen-free objects. Also, no more particles are present. The syringe is filled via the proximal end; in this case, the syringe outlet piece is sealed with a closure. The filled syringe is sealed with the plug.
After the syringe parts come out of the die, gas is blown over them to remove particles. The syringe is then washed and provided with lubricant. The syringe is then sterilized in such a way that the syringe can be further processed, stored, or transported, as desired.
Disadvantageous in the case of the known syringes is that silicone oil must be used to reduce the friction between the plug and the inside wall of the syringe. Although a rubber plug is reasonable in view of the elastic forces, behavior relative to sliding friction is problematical. Adhesive friction is even more of a problem. Especially in the case of prolonged storage of the syringe with an inserted plug, adhesive friction plays a very important role. In addition, consideration should always be given to cold-flow behavior in the case of rubber plugs. Since the latter factor is not insignificant, rubber plugs with considerable prestressing must be used. The latter is all the more important when the filled syringes with inserted rubber plugs are then autoclaved. The cold-flow behavior of the rubber plug is a function of temperature. High prestressing is necessary in this case when the plug is inserted. In this case, friction in all cases is so great that, without silicone oil, handling of the syringes is not possible.
Even if sealing lips made of rubber are used, the latter in the static state do not seal adequately or suffer from cold-flow behavior, especially during autoclaving. Also in this case, work is to be done with considerable prestressing, so that silicone oil is indispensable in this case as well.
A solid plug that is made of teflon has a considerable disadvantage in the case of syringes that are exposed to thermal stress. Here, even temperature fluctuations of from -10.degree. C. to +40.degree. C. are sufficient to allow the plastics of the syringe wall to expand relative to the very solid teflon material. Autoclaving is a stress for the plug or the syringe owing to the fact that one of the two exhibits cold-flow behavior, which causes leaks after the syringe cools. To allow the plug to seal well, great prestressing, which means great friction, is necessary because of the slightly elastic behavior of the solid teflon plug. Such a teflon plug is not to be used in plastic syringes since the cold-flow behavior of the syringe wall that is made of plastic increases the inside diameter of the syringe at the level of the plug during autoclaving. As a result, gaps form through which liquid can pass uncontrolled from the syringe. As a result, uncontrolled air can also be aspirated. Glass syringes, which do not exhibit such cold-flow behavior, must still be coated with silicone oil on the inside wall to reduce friction, which is caused by the very high prestressing. During autoclaving, such a syringe slips away from the teflon plug because of the cold-flow behavior relative to the harder glass. Also, here, gaps and splits, which can allow the syringes to become unsealed, are the result after cooling.